Production of encapsulated light-sensitive diazotype compositions and coatings



.area of the coat.

United States Patent The present invention relates to diazotypes, and in particular, to light-sensitive compositions which may be developed by heat, and otherwise.

The diazotype art requires a coating containing a lightsensitive diazo compound which under a predetermined condition combines with a correspondingly predetermined coupling agent to form a dyestuif. The light-sensitive diazo compound is such that when exposed to actinic light it decomposes to a form not capable of so coupling to form color. Consequently, a paper or other carrier base coated with such a diazo compound may be exposed to such light through a masking pattern, such as a mechanical drawing on a transparency, to leave light-sensitive diazo compound where the light is blocked by the pattern.

There are many combinations of diazo compounds and couplers. Some combinations may exist together and remain unreactive until the combination is present in a suitable acid or alkaline environment. Such a corn bination may exist in an acid, or neutral, or alkaline condition as exposed to light, and then color is developed by use of an agent to change the pH, for example, ammonia gas, an alkaline solution, or an acid solution, as required.

Where the printed paper is wetted for development, it may contain the coupler, and the solution may be acid, neutral or alkaline according to the reactivity of the diazo compound and the coupler.

In commercial practice, both liquid and gas development are employed. Special apparatus is required, as well as in the provision and maintaining of a supply or the development chemicals. However, image-development by heat is known and very desirable, but there are diiiicul- ;ties encountered in producing stable light-sensitive coatings. The compositions are not as diverse as in the cases Where liquid or as development is to be practiced.

There are desirable combinations of diazo and coupler which readily react when one in a liquid form, either melted or in solution, is in contact with the other, especially in the presence of moisture. Even though such reactive contact does not exist in a light-sensitive coat, some combinations of diazo and coupler in normal dry form and in close association, slowly couple, so that a commercial sheet coated with such a combination has poor shelf life and slowly develops background color.

The present invention relates to light-sensitive compositions including essentially a diazo compound and a coupler and in some cases, including an agent to impart or to eiiect the necessary pH condition for the coupling reaction to take place. The compositions of the present invention are such that the necessary ingredients thereof are present in close association with one or more of them encapsulated in shells each providing a barrier film so as to isolate the encapsulated material and thus prevent reaction to form color.

In addition the invention involves for the encapsulation film-forming barrier material which can be melted by heat to destroy the encapsulation and thereby etlect reaction to form color.

It is necessary that the ingredients of the composition be present in the sensitive coat in finely divided form and in substantially uniform close association throughout the Hence, the encapsulation of material sesame Patented Aug. 24 1985 requires a process capable or" applying thin barrier coats to finely divided particles and thereby providing enclosing shells. Such a process is referred to in Chemical and Engineering News, June 26, 1961, page 42, in an article entitled Vacuum Process Used To Encapsulate Solids, developed by National Research Corporation, 70 Memorial Drive, Cambridge, Massachusetts.

By that particular process, particles to be coated are exposed individually on a vibrating tray in a vacuum to a stream of vapor of the encapsulating material, so that the vapor condenses on the particles.

For the present invention, the encapsulating material is a wax or other material selected for its insolubility in a predetermined liquid vehicle which is to be used for applying the encapsulated particles or for contacting such particles in anchoring the light-sensitive coating to the carrier.

Preferably, a wax such as pa-raiiin, or micro-crystalline wax, is employed when water is used to apply the coat. A Wax or the like is used which melts at an elevated temperature, such as to avoid accidental melting of it during application or drying of the coat or in storing, handling and exposing the coated carrier. Accordingly, a melting point of at least 260 F. is preferred, so long as it is below the lowest decomposition temperature of either the diazo compound or of the coupler.

Although the invention is preferably carried out by encapsulated particles which can be suspended in water, it is to be understood that other liquids may be used in combination, including a wax insoluble in a volatile organic liquid vehicle, some oi. which combinations are described in Canadian Patent No. 627,653, of September 19, 1961, and also in copending application Serial No. 131,492, filed August 15, 1961, as a continuation-impart of Serial No. 635,946, filed January 24, 1957, now abandoned in all of which applicant is a co-inventor.

The compositions for the present invention are best developed by heat, which melts the wax or other encapsulating film, thus exposing the contents to each other for reaction. However, it is to be understood that the image to be formed may be developed otherwise. Basically, the development is to destroy the encapsulating barrier and this may be done by wetting with a solvent for the encapsulating film.

in the following examples, there are fco mbinations in which only the diazo compound is encapsulated, combinations in which only the coupler is encapsulated, combinations in which only the pH-controlling agent is encapsulated, and combinations in which both the diazo and the coupler are separately encapsulated. Of course, it is to be understood that of all the ingredients which are necessary for producing an image, only one need be encapsulated, but from one to all may be encapsulated without departing from the invention.

in the following examples where encapsulated ingredients are referred to, water is disclosed as the preferred liquid vehicle for applying the light-sensitive coat to a carrier, which is preferably paper such as is conventionally used. Paper represents a carrier which is normally dry but contains an equilibrium content of moisture. Moisture is beneficial to the speed of decomposition by light of the diazo compound, and especially beneficial to the coupling reaction. When this reaction is eiiected by heat, the heat releases free moisture from the paper and it thus performs two or more functions, namely, melt ng the encapsulating film, releasing moisture, and in some cases, melting one or both of the diazo compound and coupler to enhance the degree of intimacy for reactive contact.

Also, the compositions include a water-soluble binder, inert to the other ingredients and inert in the reaction,

merely to provide a solid coat anchored to the carrier, such binders being illustrated by gelatin, gum arabic, polyvinyl alcohol, and polyvinylpyrrolidone.

Although it is preferred to apply but one coat using a liquid containing all of the ingredients, it is within the scope of the invention to apply one coat containing a portion of all the ingredients and then over it apply a coat containing the remaining portion.

When the pH-controlling agent is encapsulated, it may be one which acts inherently to change the pH, or it may be one which decomposes when heat is applied to form th'eactive pH-controlling agent, urea, for example, being a precursor of ammonia.

The following Table I exemplifies pH-controlling agents which are encapsulated with wax for use in Water suspensions, in Case A examples being used in the sensitizing liquid, and in Case B examples being used in a precoat solution.

TABLE I In the following examples there are in the aqueous coating compositions various combinations of soluble and insoluble diazo compound and coupler. Table II lists the examples in which the encapsulated ingredient is specified as soluble or insoluble in the water.

TABLE II [Numbers refer to examples] Coupler Diazo som Insoluble Soluble Insoluble In all of the examples below standard coating technique for papers is used to apply coats having a thickness in the range from 0.5 to 1 mil, with drying below 200 F. v

for the wax employed. 7

Example 1.'Blue image Partsby weight Encapsulated o-toluidide of beta-hydroxy-napththoic p-Diazo-m-ethoxy diethylaniline zinc chloride double v salt 2 Citric acid 1 Gum arabic 1 Water Example 2.Yell0w image I Encapsulated N-acetoacetyl-alpha naphthyl'amine 6 p-Diazo-ethyl benzylaniline zinc chloride double 1 salt 1.5 Tartaric acid 1.5 Gum arabic 1. 0 Water -Q 100 Example 3.Blae image Encapsulated 2,3-dihydr0xynaphthalene 4 p-Diazo-dimethylaniline zinc chloride double salt 1.5

Oxalic acid 0.5 Polyvinyl alcohol 0.75 Water 100 Example 4.-Black image Encapsulated borofiuoride salt of p-diazo-2,5-dibutoxybenzanilide 2.0 tPhloroglucinol 1.0 Citric acid 1.0

Gelatine 0.5 Water 100 Example 5.Black image Encapsulated silicofluoride salt of p-diazo-ethylbenzylaniline 3.0 Sulfamic acid 1.0 m-Phenylenediamine 1.5 Gum arabic 1.0 Water 100 Example 6.-Red image Encapsulated p-diazo-2,5-diethoxy benzanilide zinc chloride double salt 3.5 Tartaric acid 2.0 1,3,S-phenylmethylpyrazolone 1.5 Polyvinyl alcohol 1.0 Water 100' 7 Example 7.Blue image 1 Encapsulated silicofluoride salt of p-diazo-ethylbenzylaniline 3.0 Encapsulated thiobarbituric acid 2.0 Polyvinylpyrrolidone 0.5 Diglycolic acid C 2.0 Water V ;j' 100 i I Example 8.-t -Blue image Encapsulated p-diazo-diethylaniline' zinc chloride double salt Encapsulated 2,3 dihydroxynaphthalene-o-sulfonic acid sodium salt 3.0 'Tartaric acid ..V 0.75 Gum arabic Q. 1. 0 Water 100 Example 9 .--Br0w1i image Encapsulated B-naphthylamine 2.5 Encapsulated p-diaizo-B-hydroxyethyl 'ethylaniline zinc chloride double salt -2.0 Citric acid 1.0 Gelatine 1.0

Water 100 Example 10.Purple image Encapsulated borofluoride salt of 1-diazo-2',5,4'-triethoxydiphenyl 2.0 Encapsulated 2,2',4,4-tetrahydroxybipheny1 4.0 Suliarnic acid 0.5 Gum arabic 1.0 Water 100 V V 7 Example 11 p-Diazo diethylaniline 2.0 Citric acid 1.5 2,3-dihydroxynaphthalene-6-sulfonic l acid, f sodium salt 2.5 Polyvinylalcohol 1.0 Encapsulated hexamethylenetetramine 20 Water 100 Example 12 As Example 11, but using encapsulated sodium hexylene glycol monoborate in place of hexamethylenetetrarnine.

Example 13 As Example 11, but using encapsulated urea in place of hexamethylenetetramine.

Example 14 As Example 11, but using encapsulated disodium phosphate in place of hexamethylenetetrarnine.

Example 15 As Example 11, but using encapsulated guanidine acetate in place of hexamethylenetetramine.

Example 16 As Example 11, but using encapsulated phenyl biguanide in place of hexamethylenetetramine.

Example 17 As Example 11, but using encapsulated symmetrical diphenyl urea in place of hexamethylenetetrarnine.

Example 18 Paper is coated with a suspension of the following:

Parts by weight Encapsulated hexamethylenetetramine Polyvinyl alcohol 1.0 Water 100 and air dried at a temperature not exceeding 200 F. This is then subsequently coated with:

Parts by weight p-Diazo diethylaniline 2.0 Citric acid 1.5 2,3-dihydroxy-6-naphthalene-sulfonic acid, sodium salt 2.5

Water 100 Example 19 As Example 18, but substituting encapsulated sodium hexylene glycol monoborate for hexamethylenetetramine in the precoat.

Example 20 As Example 18, but substituting encapsulated urea for hexamethylenetetramine in the precoat.

Example 21 As Example 18, but substituting encapsulated disodium phosphate for hexamethylenetetramine in the precoat.

Example 22 As Example 18, but substituting encapsulated guanidine acetate for hexamethylenetetramine in the precoat.

Example 23 As Example 18, but substituting encapsulated phenyl biguanide for hexamcthylenetetramine in the precoat.

Example 24 As Example 18, but substituting encapsulated symmetrical diphenyl urea for hexamethylenetetramine in the prccoat.

The barrier material is not limited to hydrocarbon waxes, nor to chemically inert materials. Stearic acid is wax-like and insoluble in water, but soluble in alkali, so as to form sodium, ammonium, or amine soaps. Consequently, a coat having it as the encapsulating barrier can be developed by heat, by alkaline solution, and by organic solvents for stearic acid. Higher alcohols which are insoluble, such as stearyl alcohol, likewise may be used.

The encapsulating process referred to is highly versatile, as indicated by the fact that polystyrene spheres may be encapsulated with aluminum. Metals such as zinc, magnesium, cadmium, chromium, nickel, tin, gold and silver may encapsulate particle material. Consequently,

a Wide variety of materials which can be melted in thermally developing diazotypes, may be used in the present invention, within the scope of the appended claims.

I claim:

1. A light-sensitive diazotype composition in a dry coat on a carrier base comprising all the ingredients which together effect the formation of an image at an elevated temperature, including a solid light-sensitive diazo compound and a solid coupling agent therefor, at least one of the ingredients being encapsulated finely divided particles thereof within shells of normally solid film-forming material which melts at said elevated temperature.

2. A light-sensitive diazotype composition in a coat on a carrier base according to claim 1 in which the filmforrning material is a water-insoluble wax melting at a temperature of at least 200 F.

3. A light-sensitive diazotype composition in a coat on a carrier base according to claim 1 in which the filmforrning material is stearic acid.

4-. A light-sensitive diazotype composition in a coat on a carrier base according to claim 1 in which the diazo compound is the encapsulated ingredient.

5. A light-sensitive diazotype composition in a coat on a carrier base according to claim 1 in which the coupling agent is the encapsulated ingredient.

6. A light-sensitive diazotype composition in a dry coat on a carrier base comprising a solid light-sensitive diazo compound, a solid coupling agent reactive therewith at an elevated temperature and at a predetermined range of pH and unreactive therewith outside of said range, and a pH-controlling compound in finely divided form encapsulated in minute shells of film-forming material which melts at said elevated temperature, said pH-controlling compound on release from said shells at said elevated temperature being active to effect a pH in said range, whereby said diazo compound and said coupling agent react.

7. A light-sensitive diazotype composition in a coat on a carrier base according to claim 6 wherein said pH-controlling compound is an alkaline agent.

3. A light-sensitive diazotype composition in a coat on a carrier base according to claim 6 wherein said pH-controlling compound is selected from the group consisting of hexamethylenetetrarnine, sodium hexylene glycol monoborate, urea, disodium phosphate, guanidine acetate, phenyl biguanide and symmetrical diphenyl urea.

9. The method of forming a light-sensitive coat including a light-sensitive diazo compound and a coupling agent there-for, which method comprises encapsulating within shells of barrier film-forming material finely divided particles of at least one of all of the ingredients of a light-sensitive diazotype coating which together at an elevated temperature form an image, said film-forming material being normally solid and fusible at said elevated temperature, applying all of said ingredients in a thin layer to a carrier base in a volatile liquid vehicle in which said film-forming material is insoluble, and evaporating the liquid to form a light-sensitive thin coat subject to color-formation on heating to a temperature to melt said film-forming material.

lit. The method of claim 9 in which the diazo compound is encapsulated.

11. The method of claim 9 in which the coupling agent is encapsulated.

12. The method of claim 9 in which both the diazo compound and the coupling agent are separately encapsulated.

References Cited by the Examiner UNITED STATES PATENTS 2,634,677 4/53 Klimkowski et al. 96-91 XR 2,732,299 1/56 Morrison 9676 X (Uther references on following page) V UNITED STATES PATENTS ,FOREEGN PATENTS 1,041,980 10/58 German Frederick -3 9675 Land. V

Ti v NORMAN G. TORCI-IIN, Primary Examiner. Foris X PHILIP E. MANGANExfaminer.

Macaulay.

Lindquist et a1. 9676 X Sagura et a1 9649 

1. A LIGHT-SENSITIVE DIAZOTYPE COMPOSITION IN A DRY COAT ON A CARRIER BASE COMPRISING ALL THE INGREDIENTS WHICH TOGETHER EFFECT THE FORMATION OF AN IMAGE AT AN ELEVATED TEMPERATURE, INCLUDING A SOLID LIGHT-SENSITIVE DIAZO COMPOUND AND A SOLID COUPLING AGENT THEREFOR, AT LEAST ONE OF THE INGREDIENTS BEING ENCAPSULATED FINELY DIVIDED PARTICLES THEREOF WITHIN SHELLS OF NORMALLY SOLID FILM-FORMING MATERIAL WHICH MELTS AT SAID ELEVATED TEMPERATURE. 